Above the floodplain, much of the habitat in the watershed consists of mixed conifer forest. Trees and shrubs, including stands of red alder and cottonwood trees, cover about 88 percent of the middle reaches.[34] Near the headwaters, the forests consist mainly of mixed conifers and hardwoods with a few older Douglas-firs. Common species include big leaf maple, willow, western hemlock, red alder, western red cedar, and Douglas-fir.[34] Most of this forest is relatively young. In Forest Park, old growth forest, undisturbed for 250 years or more, exists mainly in isolated patches.[35] The largest tree in the park is a Douglas-fir near the Stone House. It is 242 feet (74 m) high, and the trunk is 17.3 feet (5.3 m) in circumference.[36]